1. Field of the Invention
Embodiments disclosed herein generally relate to well drilling operations and more particularly to locating a casing or drill string of a first wellbore from a second wellbore while drilling the second wellbore. More specifically, embodiments disclosed herein relate to electric current and magnetic signals used in locating or detecting casing.
2. Background Art
In various drilling operations it is desirable to locate adjacent wellbores. Examples of drilling operations that may require locating adjacent wellbores include relief well drilling, drilling U-shaped wells, and steam assisted gravity drainage (SAGD) operations. From time to time, wells blowout, and it is desired to kill the well subsurface. Thus, it is necessary to accurately position the first well while drilling the second intercepting relief wellbore. Another common application for locating adjacent wellbores occurs when drilling a second wellbore substantially parallel to a first wellbore such as in SAGD wells.
Current methods for locating casing (or drill string) of a first wellbore use wireline tools. Conducting locating surveys utilizing wireline tools, and relying on those results, has significant drawbacks. For example, using wireline equipment increases rig time and costs. Further, wellbore location information is only obtained periodically with these wireline methods. This unavailability to have constant, timely and accurate data can result in significant and costly errors.
Intercepting an exiting wellbore with a second well is used for killing blow-outs and for drilling “U-shaped wells.” In a blow-out, the first well encounters an unexpectedly high pressure formation during drilling. If the weight of the drilling mud is too low, the formation pressure exceeds the borehole pressure and fluids from the formation enter the wellbore in an uncontrolled manner. The formation fluids blow the drilling mud out of the annulus between the formation and the drill string. Because the formation fluids are less dense than the mud, the pressure at the surface can become very high. This is a serious situation that may endanger people and the environment and that may damage the drilling rig and the reservoir.
If standard drilling control methods (e.g., “weight and wait”) cannot reestablish a greater pressure in the borehole than in the formation, the extreme measure of drilling a relief well is undertaken. A second wellbore is drilled from an offset location and attempts to intercept the first well a short distance above the blown-out formation. Wireline magnetic ranging methods are used when a drilling the relief well. The BHA in the second well is periodically removed and a wireline tool is run in the open hole of the relief well (see U.S. Pat. No. 4,372,398) to determine the distance and direction to the well to be intercepted. The wireline tool of U.S. Pat. No. 4,372,398 has two widely spaced, current injecting electrodes, and a sonde with a magnetometer located below them. The injected current concentrates on the drill string in the first well, and the resulting magnetic field is measured with the magnetometer to determine the relative bearing of the first well with respect to the second well. By taking several bearings at different locations in the relief well, it is also possible to determine the distance to the blow-out. Eventually, the relief well is able to intercept the blow-out, but this may require a large number of trips, i.e., the drill string is removed and a wireline magnetic ranging tool is run into the open hole. Each trip may require one or more days of rig time, so the process can be very slow and expensive. The relief well has a very heavy mud that can “kill” the blow-out by reestablishing a borehole pressure greater than the formation pressure.
A second application for intercepting a first wells from a second well is to create a “U-shaped” well. Two horizontal wells are drilled from different locations and intercept “toe-to-toe” underground (see “First U-tube well connects horizontal wells”, Drilling Contractor, September-October 2005). One purpose for drilling a U-shaped well is to lay cables or pipelines under a river. Another purpose is to provide a pipeline from land to an offshore well, where the stability of the seafloor cannot support a seafloor pipeline. Another purpose may be to produce heavy oil through hot subsurface formations, rather than through a seafloor pipeline exposed to cold water. Cold pipelines increase the viscosity of the heavy oil and may prevent its production. To drill a U-shaped well, a first well is drilled and cased. As the second well is drilled and approaches the end of the first well, a wireline tool must be inserted in the first well for magnetic ranging. This requires a rig be maintained on the first well to deploy the wireline tool in the horizontal well.
Therefore, it is a desire to provide an adjacent well locating device and method that addresses drawbacks of the prior art locating devices and methods. It is a still further desire to provide an adjacent well locating device and method with measurement while drilling (“MWD”).